IBM’s solar tech is 80% efficient thanks to supercomputer know-how

Water that cools photovoltaics gets used for other purposes, upping efficiency.

By borrowing cooling systems used in its supercomputers, IBM Research claims it can dramatically increase the overall efficiency of concentrated photovoltaic solar power from 30 to 80 percent.

Like other concentrated photovoltaic (CPV) collectors, IBM's system at its Zurich laboratory uses a mirrored parabolic dish to concentrate incoming solar radiation onto PV cells. The dish uses a tracking system to move with the sun, concentrating the collected radiation by a factor of 2,000 onto a sensor containing triple-junction PV cells. During daylight hours, each 1-sq cm PV chip generates on average between 200 and 250 watts of electrical power, harnessing up to 30 percent of the incoming solar energy.

Ordinarily, the remaining 70 percent of energy would be lost as heat. But by capturing most of that heat with water, IBM Research says it is able to reduce system heat losses to around 20 percent of the total incoming energy. This results in a bottom-line efficiency of 80 percent for its CPV collector, dubbed HCPVT for High Concentration Photovoltaic Thermal. Unlike a regular CPV system, HCPVT delivers its energy in two forms: electricity and hot water.

The thermal system was adapted from IBM Research's 6-teraflop Aquasar supercomputer, which went online at ETH Zurich in 2010. By using water as a coolant, Aquasar consumes three fifths of the energy of a comparable air-cooled machine of the time. Crucially, the hot water could be put to work heating university buildings, reducing Aquasar's carbon footprint to a claimed 15 percent of what would otherwise have been the case.

As with Aquasar, micro-channels between 50 and 100 micrometers in diameter carry water exceptionally close to the source of heat: the processing units in the case of Aquasar, the PV cells here. Thermal resistance is reduced to a tenth of competing systems with larger water channels.

"This allows us to cool with hot water, which sounds a bit strange," IBM scientist Dr. Bruno Michel told Ars during a Skype call. "The photovoltaic chip is around 100º [centigrade] while the coolant is 90º."

To live up to its efficiency, the HCPVT system needs to put its hot water to good use. Though outside the scope of this team's work, IBM Research is also looking at systems which could use the heat by-product to purify water or, somewhat counterintuitively, to cool buildings using adsorption refrigeration.

The team has developed a prototype with a 4×4-cm PV receiver which generates about 1kW of electrical power. It hopes to develop a much larger HCPVT system with a 100-sq m dish and a 25×25 cm receiver, producing 25kW of electrical power and 50kW of thermal power. (Larger PV receivers have gaps between the chips, so you don't gain an additional 200W of electrical power for every square centimeter of receiver you add.)

In a YouTube video, Dr. Michel raises the possibility that these larger HCPVT collectors could one day be used to build solar power stations in, say, the Sahara Desert. According to the team's calculations, covering 2 percent of the area of the Sahara with HCPVT would meet the world's electricity needs, transmission issues aside. Not that you need a desert. Michel told Ars that the system is useful almost anywhere where you have direct solar radiation—Zurich, for instance. "By adding the thermal output we can extend its range of applications compared to CPV," he said.

The HCPVT system has been in development for more than 5 years, initially in collaboration with the Egypt Nanotechnology Research Center.

IBM's description of the new system.

James Holloway
James is a contributing science writer. He's a graduate of the Open University, with a B.Sc. in Technology and a Diploma in Design and Innovation. Twitter@jamesholloway

"According to the team's calculations, covering 2 percent of the area of the Sahara with HCPVT would meet the world's electricity needs, transmission issues aside. "

Yes, and a flying unicorn could meet all of my transportation needs, reality issues aside.

Anyway, cool tech, glad that we are continually improving PV performance characteristics. Wonder if the dual electrical/thermal output might make this attractive for home installations? Though the tracking requirement adds installation complexity.

So....going to use the hot water in the sahara desert? Sure using waste heat for heating purposes can do good. The application is the problem. I really isn't news - PV + heater has been around since PV has been around.

How much does it cost per MW? 30% vs 20% for standard PV. Tracking sun = extra cost in setup, running, and maintenance. If it cost 5x as much wouldn't it be better to push out 5x the panels at 20%? Than one panel at 30%?

80%, that is rather remarkable. Assuming the full amount of retained energy could be put to good use. The endgame will be to use smart engineering to put all that energy to real life use in an economical and practical manner.

Electricity is a much higher grade and more valuable form of energy than 90C water ... very different exergy. Maybe you can use the 90C water for heating, or absorption chillers as described in the article, but no chance of converting it into electricity - simply not high grade enough.

(edit: as Maury points out upthread, even in the best case with magic hypothetical technology that could convert 90C water into electricity, only 30% conversion of heat ...)

How much does it cost per MW? 30% vs 20% for standard PV. Tracking sun = extra cost in setup, running, and maintenance. If it cost 5x as much wouldn't it be better to push out 5x the panels at 20%? Than one panel at 30%?

Actually the real question, going on real-world experience here, is how much does the tracker cost?

Some time ago I was on a call where Emcore was pitching their CPV system for an install in Thunder Bay. They said they were making the cells at $1 per watt, at a time when a typical panel was in the $2 to $2.50 range.

Then I asked how much the tracker would add to that. $7 a watt. That was more than *complete systems* were going in for.

The reasons the trackers cost so much is pure geometry. You're focusing a large area onto a tiny one, at short ranges. So as the sun moves, the focused spot is moving that many times faster, which you have to track *very* accurately. We're talking large telescope accuracies here. It ain't cheap.

As is almost always the case in these press releases, the devil is in the details.

Of the 100% of incoming power, 80% is captured in total. 30% turns into electricity, so that leaves 50% as heat.

Even with the best processes, you *might* get 30% of that as electricity. You have to convert it to steam and then spin it in a turbine.

So the total collection would be 30 + (50 * .3) = 45%

Emcore (claims to) make cells that are 40% efficient, directly. So this isn't much of an advance.

Depending on the application it could be much more efficient than that when the heated water is used to heat something directly or simply used for hot water applications instead of attempting to harness electricity.

Heating water isn't especially energy efficient and heated water is broadly used for either radiator heat or washing and showering. Energy saved by simply using the hot water rather than heating water is energy harnessed all the same.

Seems to me that this would be nice and efficient in cold weather when you need direct heat, but on hot summer days the heat goes to waste (unless it's converted to electricity with the limit being the Carnot limit -- and from what it looks like, this system does not include heat-to electricity conversion).

So -- Switzerland might not be too bad, but the Sahara? No way (unless the heat could then somehow be used for desalinization)

Am I the only person that saw this, and immediately thought "hey, no need for a hot water heater in my house!".

In a typical home, the hot water heater is one of the largest sinks of electrical power. Ditch the need for that, and suddenly you need fewer PV cells to power your home.

Seems like a win/win, unless I'm missing something.

Not just you - that's the first thing I thought of. Clearly it would not replace your hot water heater, as even solar collectors don't do that. But if this unit could easily combine a PV and hot water collector that would be pretty awesome.

Not sure that this would be cheaper than a standard system of panels + collectors though.

Electricity is a much higher grade and more valuable form of energy than 90C water ... very different exergy. Maybe you can use the 90C water for heating, or absorption chillers as described in the article, but no chance of converting it into electricity - simply not high grade enough.

(edit: as Maury points out upthread, even in the best case with magic hypothetical technology that could convert 90C water into electricity, only 30% conversion of heat ...)

The magical technology is called a Stirling engine. Not sure what kind of efficiency it can get with a 90ºC hot side and a room temperature cold side.Then again, maybe the PV cells can be made to operate at higher temperatures.

Am I the only person that saw this, and immediately thought "hey, no need for a hot water heater in my house!".

In a typical home, the hot water heater is one of the largest sinks of electrical power. Ditch the need for that, and suddenly you need fewer PV cells to power your home.

Seems like a win/win, unless I'm missing something.

Well, electricity is a pretty terrible way to heat a house. Natural gas is much cheaper and more energy efficient. So for example, virtually every house in the UK has a natural gas boiler for providing heating.

If you want to heat a house by solar energy, a passive solar water panel would be almost 100% efficient

Electricity is a much higher grade and more valuable form of energy than 90C water ... very different exergy. Maybe you can use the 90C water for heating, or absorption chillers as described in the article, but no chance of converting it into electricity - simply not high grade enough.

Agreed. I'm not even convinced absorption chillers would be particularly efficient. Still might make economic sense, but you'd have to adjust the efficiency stat to be equivalent to using traditional electric chillers, which as you point out would bring that 80% level down (probably dramatically).

The real win on this kind of tech would be to implement it somewhere where you can make efficient use of 90C water. What about on the roof of a hotel? Most hotel hot water is used in the morning, then you could reheat the water in a big tank using this during the day. You would need a supplemental heater for cloudy days, but it still might be a big win. There might be industrial uses where relatively cheap 90C water would be a boon, also.

Am I the only person that saw this, and immediately thought "hey, no need for a hot water heater in my house!".

In a typical home, the hot water heater is one of the largest sinks of electrical power. Ditch the need for that, and suddenly you need fewer PV cells to power your home.

Seems like a win/win, unless I'm missing something.

Well, electricity is a pretty terrible way to heat a house. Natural gas is much cheaper and more energy efficient. Which is why, for example, virtually every house in the UK has a natural gas boiler for providing heating.

If you want to heat a house by solar energy, a passive solar water panel would be almost 100% efficient [/quote]

My take away from this is concentrated solar power will bring back the state flower of West Virgina - the satellite dish - where a 4x4cm will generate enough power to power your house. When you think about it this is probably the best solar design. Rather than a roof of flat panels you have one or two 2m dishes that are cheaply constructed. The only expensive part is that small 4x4cm converter.

The article makes it sound like a big breaktrough.90°C water? It has little to no use besides heating a building. In the industry it's usually a hassle dealing with water this hot, you have to cool it in artificial ponds before reusing it or dumping it.

And for homes, there are cheap water heating solutions already avaiable.

Not just you - that's the first thing I thought of. Clearly it would not replace your hot water heater, as even solar collectors don't do that. But if this unit could easily combine a PV and hot water collector that would be pretty awesome.

Not sure that this would be cheaper than a standard system of panels + collectors though.

Well, like anything you'd have to do the cost-benefit analysis for the life of the system, factoring in the cost savings over a traditional water heater (I'm not sure how long a quality water heater lasts--I'm guessing maybe it would be replaced once in the lifespan of your average home PV installation) and other heating system (if you're thinking of replacing the furnace as well). It would probably need to be a uniquely developed hybrid system of some sort for heat availability at night, but the potential is definitely there. Man, where was this when I was in school? This would have been a great senior design project!

In a YouTube video, Dr. Michel raises the possibility that these larger HCPVT collectors could one day be used to build solar power stations in, say, the Sahara Desert. According to the team's calculations, covering 2 percent of the area of the Sahara with HCPVT would meet the world's electricity needs, transmission issues aside.

"According to the team's calculations, covering 2 percent of the area of the Sahara with HCPVT would meet the world's electricity needs, transmission issues aside. "

Yes, and a flying unicorn could meet all of my transportation needs, reality issues aside.

Anyway, cool tech, glad that we are continually improving PV performance characteristics. Wonder if the dual electrical/thermal output might make this attractive for home installations? Though the tracking requirement adds installation complexity.

I knew a guy in San Antonio who had a sizable solar array that tracked the sun using a cylinder of gas (not sure what type) and a heat collecting plate. The system was basically an actuator. The plate absorbs heat and expands gas on one side of the cylinder. It drives a piston on a shaft that slowly turned the array to follow the sun. When the sun sets and the gasses cool, the array would automatically reset.

I'm sure there was a bit of calibration involved but once set up, it was relatively maintenance free and didn't sap the electricity he was producing. I'm not sure about the window of time when he was able to get the most efficiency out of his array with this system.

Well, electricity is a pretty terrible way to heat a house. Natural gas is much cheaper and more energy efficient. So for example, virtually every house in the UK has a natural gas boiler for providing heating.

If you want to heat a house by solar energy, a passive solar water panel would be almost 100% efficient

While electric heating is 100% efficient (use of electricity once it gets to your house. Not so much if starting from coal), you can do better than a boiler by using a heat pump for a fairly wide range of outdoor temperatures (since you are moving entropy instead of creating it, you can have effective efficiencies of >100%. If you use a ground-based heat pump, you can get even higher efficiencies all year round.

I don't think anyone has made glass with the insulation needed to make passive solar work. PV+[ground based] heat pumps give you air conditioning as well (especially needed in places where solar works well).

Cogeneration efficiencies are often 80% +. The thing is that thermal efficiency claims for cogeneration systems are a bit deceiving because you get both electricity and thermal energy out – and they are not equivalent forms of energy.

As with Aquasar, micro-channels between 50 and 100 micrometers in diameter carry water exceptionally close to the source of heat: the processing units in the case of Aquasar, the PV cells here. Thermal resistance is reduced to a tenth of competing systems with larger water channels.

I'm assuming that you need to use distilled water as any impurities like lime scale will block the mirco-channels. So do you then have to transfer the heat to usable tap water with a heat exchange?

...covering 2 percent of the area of the Sahara with HCPVT would meet the world's electricity needs...

The Sahara is kind of a big place. I'm guessing we run out of heavy metals, and hell, probably even aluminum, before that happens. But beyond that, this is good news. And one of the real advantages of solar is the ability to put collectors close to the point of usage, eliminating all those transmission costs.

...covering 2 percent of the area of the Sahara with HCPVT would meet the world's electricity needs...

The Sahara is kind of a big place. I'm guessing we run out of heavy metals, and hell, probably even aluminum, before that happens. But beyond that, this is good news. And one of the real advantages of solar is the ability to put collectors close to the point of usage, eliminating all those transmission costs.

If there was only a way to make sand into glass, which could make the bulk of the structural material. But where would you get all that sand? ;-)

So for example, virtually every house in the UK has a natural gas boiler for providing heating.

If you want to heat a house by solar energy, a passive solar water panel would be almost 100% efficient

Efficient, perhaps, but effectiveness is a fair question. Most of the places that get really cold also get a much lower level of sunlight, especially so during the short, darker days of winter. At maybe 52° North latitude, your English locations need quite a bit more area than the hypothetical Sahara installation that —surprise!— doesn't need heating.

Er, uh, if such big energy gains are to be acquired by doing this in the Sahara, how many of those gains are lost by transporting water to enable the process through which those gains are acquired? Eh?

I knew a guy in San Antonio who had a sizable solar array that tracked the sun using a cylinder of gas (not sure what type) and a heat collecting plate. The system was basically an actuator. The plate absorbs heat and expands gas on one side of the cylinder. It drives a piston on a shaft that slowly turned the array to follow the sun. When the sun sets and the gasses cool, the array would automatically reset.

I'm sure there was a bit of calibration involved but once set up, it was relatively maintenance free and didn't sap the electricity he was producing. I'm not sure about the window of time when he was able to get the most efficiency out of his array with this system.

That type is fine for a traditional solar array that is pointed at the sun, but in this case you need more accuracy, since a small tracking error will cause the focused rays of the sun to land some other than the 4x4cm PV--which will drop the power output to near 0% and possibly damage whatever the dish IS focused on.

The problem I see with most of these PV breakthroughs in a home setting is that they don't come close to the efficiency of a simple solar water heater. And adding plumbing to existing construction is even easier now with flexible tubing like PEX.

As is almost always the case in these press releases, the devil is in the details...

...So the total collection would be 30 + (50 * .3) = 45%

Emcore (claims to) make cells that are 40% efficient, directly. So this isn't much of an advance.

I must agree- efficiency claims above 50% should raise warning flags. I think you can construe the accounting to reach this figure, but I don't think it means that of 100W of sunlight that reach the collector, enough electricity would be generated to power an 80W light bulb.

Lots of houses north of 50 degrees can get most of their hot water for a lot of the year from solar thermal heating. I'm not sure why more people don't do it, probably cost of installation/integration with gas/oil heating systems.

PV systems in the sahara might get away without using a heliostat system. Losing some efficiency might mean they would need less cooling.